1. Field of the Invention
The present invention relates to a cooling water passage structure in a cylinder head of an internal combustion engine.
2. Description of the Related Art
A multi-cylinder engine is generally constructed such that a plurality of intake ports and a plurality of exhaust ports are formed inside a cylinder head, and an intake manifold for distributing intake air and an exhaust manifold for collecting exhaust gases are connected respectively to an intake-side lateral surface and an exhaust-side lateral surface of the cylinder head. In another known construction, an exhaust collecting portion for collecting exhaust gases is also formed inside the cylinder head, and a single exhaust pipe is connected to the exhaust-side lateral surface of the cylinder head. The multi-cylinder engine provided with the exhaust collecting portion formed inside the cylinder head has the following advantages. Because of no need of separately providing the exhaust manifold, the size of the entire engine can be reduced. Further, because heat released from the exhaust gases can be suppressed, the catalyst temperature can be more quickly raised for earlier activation in warming-up. However, the exhaust gases need to be properly cooled in order to prevent thermal deterioration of a catalyst, which may be caused due to an excessive temperature rise.
Additionally, in the cylinder head provided with the exhaust collecting portion formed therein, when a large cooling water passage is formed around the exhaust collecting portion, a boss portion for a bolt for fastening the cylinder head to a cylinder block is surrounded by the cooling water passage, and hence rigidity of the boss portion for the bolt is reduced. To overcome such a problem, an invention is proposed in which a reinforcement is formed in the cooling water passage for the cylinder head such that the reinforcement is projected from the boss portion for the bolt into the cooling water passage in a direction in which combustion chambers are arrayed, and the reinforcement is extended in a direction in which the bolt is fastened (see Japanese Unexamined Patent Application Publication No. 2009-221988).
Meanwhile, there is known a concept for increasing an effect of cooling the cylinder head by forming a cooling water passage inside the cylinder head to extend along a plurality of combustion chambers, and by providing a deflector in an upper wall portion defining the cooling water passage, i.e., in a wall portion of the cooling water passage on the side opposite to the combustion chambers, the deflector deflecting a flow of cooling water such that the cooling water is caused to pass along a lower portion defining the cooling water passage, i.e., along a wall surface of the cooling water passage closer to the combustion engines (see Japanese Examined Utility Model Registration Application Publication No. 47-24533 and Japanese Examined Patent Application Publication No. 56-148647).